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Dog Medication Dosage: Ask Your Vet First

Thinking of giving your dog Benadryl, Pepcid or another human medicine? The safe dose depends on your dog, not just their weight, so start with a call to your vet.

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What your vet may use, not a dose for your dog

These are the published veterinary ranges for two common human medicines. Your vet chooses where in the range, or whether to use the medicine at all, based on your dog's health, other medicines and the exact product. Please don't give either one without asking your vet first.

Diphenhydramine (plain Benadryl)

Published veterinary range: 2 to 4 mg per kg of body weight (about 0.9 to 1.8 mg per pound), by mouth, every 8 to 12 hours as needed.

What vets use it for: Allergic skin conditions and hives. Vets also use it for nausea and motion sickness, sometimes at a different interval.

Cautions:

  • Merck lists heart disease and glaucoma as reasons not to use this group of antihistamines, and warns it can cause urinary retention.
  • It can cause drowsiness, vomiting or diarrhea. Merck notes an overdose can cause dangerous overexcitement and may be fatal.
  • Use plain diphenhydramine only. Products with a decongestant (such as pseudoephedrine or phenylephrine), a pain reliever such as acetaminophen, or xylitol can be dangerous to dogs.

Source: Merck Veterinary Manual, Antihistamines for Integumentary Disease in Animals

Famotidine (Pepcid)

Published veterinary range: 0.5 to 1 mg per kg of body weight (about 0.23 to 0.45 mg per pound), by mouth, once a day.

What vets use it for: Reducing stomach acid, for example with stomach ulcers.

Cautions:

  • Merck notes dogs can become tolerant with long-term use, and stopping suddenly can make stomach acid rebound. Ask your vet how to stop.
  • Use plain famotidine. Combination products such as Pepcid Complete also contain antacids.
  • Vomiting blood, black or tarry stools, or vomiting that keeps going need a vet, not an antacid.

Source: Merck Veterinary Manual, Drugs Used to Treat Gastrointestinal Ulcers in Monogastric Animals

Pepto-Bismol, melatonin and fish oil: no standard per-weight dose for dogs is published (Merck says of Pepto-Bismol, "There is no precise dose for animals"). Ask your vet.

Hydrogen peroxide to make a dog vomit: only under a vet's or poison line's guidance (ASPCA). Never for cats.

If your dog swallowed a medicine or something toxic, call your vet, an emergency clinic or an animal poison line now. Pet Poison Helpline (1-855-764-7661) serves Canada 24/7; a fee applies.

Important Safety Notes

Before giving any OTC medication

  • Call your vet -- especially if your dog takes other medications
  • Check the label for xylitol, pseudoephedrine, or acetaminophen -- all are toxic to dogs
  • Weigh your dog accurately -- guessing can lead to overdose
  • Use only the product and dose your vet gives you
  • Never give human cold/flu combination medications

Medications that are NEVER safe for dogs

  • Ibuprofen (Advil, Motrin) -- causes kidney failure
  • Acetaminophen (Tylenol) -- causes liver damage
  • Naproxen (Aleve) -- causes GI bleeding and kidney failure
  • Pseudoephedrine (Sudafed) -- causes seizures, death
  • Any product containing xylitol

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Frequently Asked Questions

Can I give my dog Benadryl?
Sometimes, but only with your vet's direction. Vets do use diphenhydramine (Benadryl) in dogs, and the right dose depends on your dog's weight, health and other medicines, so ask them for the amount. The key word is plain -- you must use a product that contains only diphenhydramine as the active ingredient. Many combination products include decongestants like pseudoephedrine or sweeteners like xylitol, both of which are toxic to dogs. Always check the label and consult your vet before the first dose, especially if your dog takes other medications.
Is Pepto-Bismol safe for dogs?
Ask your vet first. Pepto-Bismol (bismuth subsalicylate) contains a salicylate, the same family as aspirin, so the right dose depends on your dog's size, health and other medications, and very small dogs are easy to overdose. We removed it from the calculator while a vet reviews our numbers. It also turns stool dark or black, which can hide bleeding your vet needs to know about. Never give it to cats, or to dogs taking aspirin or other NSAIDs.
When should I use hydrogen peroxide to make my dog vomit?
Only if your vet or an animal poison line tells you to, and only at the exact dose they give you for your dog. We removed it from the calculator while a vet reviews our numbers. If your dog does not vomit, do not give more without asking; go to the emergency vet. Never induce vomiting if the dog swallowed something sharp (it could tear the esophagus on the way up), caustic (bleach, drain cleaner), or petroleum-based (motor oil, gasoline).
How much melatonin can I give my dog?
Ask your vet for a dose. There is no standard veterinary dose by weight for anxiety or sleep, so we removed melatonin from the calculator while a vet reviews it. If your vet recommends it, use plain melatonin: many human products contain xylitol or other ingredients that are dangerous to dogs.
What is the correct fish oil dose for dogs?
Ask your vet. Studies have used a range of EPA+DHA doses for different conditions, and there is no single standard, so we removed fish oil from the calculator while a vet reviews it. When comparing products, look at the EPA+DHA per capsule, not the total fish oil: a 1000 mg capsule contains much less EPA+DHA than 1000 mg.
Should I call the vet before giving my dog any OTC medication?
Yes -- always. Even common over-the-counter medications can interact with prescription drugs, worsen certain health conditions, or be dangerous at incorrect doses. Your vet knows your dog's full medical history. Some dogs have liver or kidney conditions that change how medications are processed. When in doubt, call first.